The present invention relates to a printing method and the resulting product and more particularly relates to a method for printing on composite substrates of the type consisting of fibers or fabric impregnated with a resin.
Composite materials are becoming more widely used because of their versatility and mechanical characteristics. Composite materials were originally developed by the defense and aerospace industry for high technology applications. However, in recent years these materials are becoming utilized in a wide range of applications such as for use as arrow shafts, golf club shafts, fishing rods, baseball bats, airframe structure, tool handles, boat hulls as well as many others. Generally composites consist of either fibers or woven fabric with a matrix-treated or impregnated with a resin. The resin is generally a polymer and may be a thermosetting or thermo plastic material. Thermosetting modified epoxies are often used as the matrix resin to create a composite substrate having the desired mechanical properties of tensile strength, tensile modulus, shear strength, flexural strength, flexural modulus, compression strength and compression modulus. One particularly useful type of composite is termed the xe2x80x9ccarbon pregxe2x80x9d or xe2x80x9cprepreg.xe2x80x9d These terms refer to a material having a carbon substrate, generally a dry uni-directional carbon fiber, which is impregnated with low-temperature-curing thermosetting epoxies.
These composite substrates, which will be generally referred to as xe2x80x9cprepregsxe2x80x9d or xe2x80x9cpregsxe2x80x9d are often fabricated into tubular structures such as arrow shafts, golf shafts, fishing rods and other items as mentioned above. Manufacturers of these items often wish to apply graphics such as logos, manufacturer""s names or aesthetically enhancing designs to the surface of these items. However, these types of composite substrates, and particularly carbon and carbon pregs, do not lend themselves to conventional printing techniques. These substrates are generally fragile and will easily disintegrate or degrade prior to their being fabricated into a finished product. Therefore it is not practical using current technology to apply images to these types of substrates in sheet or roll form prior to fabrication. Once the item has been formed into a finished or semi-finished product, such as a rod or tube, the resulting shape does not lend itself to printing. Further, the completed product has a surface which is generally resistant to application of printing inks, paints and other decorative material. Pad and silk-screening processes have been used to some extent.
A search of the prior art indicates there is very little prior art in the area of printing or applying graphics to composite substrates, other than decals and wraps, particularly substrates of the carbon prepreg type.
In U.S. Pat. No. 5,090,149 is representative of the prior art approach of applying designs, graphics or images to the surface of an item such as a tubular, cylindrical carbon fiber rod. The prior art approach has been to provide a flexible wrapper having a predetermined design thereon. The wrapper is wound around the outer surface of the tubular rod and covered with a transparent preservative coating such as varnish, lacquer, shellac or polyurethane. Such a procedure is expensive, time consuming and increases the weight of the ultimate product. The latter has particular disadvantages in products such as golf club shafts.
In view of the foregoing, there exists the need for a printing process which will allow graphic images or designs to be applied directly to a substrate, such as a prepreg, prior to fabrication into a completed item. Accordingly, the present invention provides a process in which the resulting fabricated item such as a tube, cylinder or flat or curved surface, once formed, displays high quality graphic images without the requirement of externally applying a decal, wrapper or covering to the item.
Briefly, the present invention provides a process for printing on composite substrates, particularly composite substrates of the type having a matrix impregnated with a resin such as a thermosetting modified epoxy. The process has particular application to carbon fiber impregnated substrates of the type known as pregs or prepregs. Such substrates, are fragile and will degrade under higher temperatures. According to the present invention, the composite substrate is maintained in a cold condition, preferably below 40xc2x0 F. Preferably the substrate material is maintained in a refrigerated condition subsequent to manufacture and is generally provided to the printer in roll form. Upon receipt by the printer, the material is sheeted into sheets from a roll. If the material has not been provided with a backing or carrier such as a release liner of paper is applied to one surface and adhered by application of pressure creating a laminate assembly. If necessary, the substrate with the liner is trimmed so that the substrate does not extend beyond the edges of the liner so as to prevent damage and unraveling of the substrate. The surface of the substrate is then coated with a top coating, which provides a base for the image. The coating may be applied by brushing, spraying, rolling or screening application. Preferably the base coating is a UV (ultra violet) curing ink. The base coating is cured and thereafter the coated surface may be printed with any desired graphic image by any number of printing processes such as lithography, screen printing, rotary letter press, flexography, rotogravure or web printing. UV curable inks, as for example containing acrylates photoinitiators, pigments, titanium dioxide and carbon black. The graphics, once applied, are cured by exposure to UV. When the printing and curing operations are completed, the printed composite substrates are returned to cold storage, preferably below 40xc2x0 F. and maintained in the cold storage, ready for subsequent processing into items such as tubes, cylinders or flat or curved surfaces on which the outer surface will display the graphic images.